1. Field of the Invention
This invention relates to hydrophobic polyurethane foams. Specifically, the invention relates to a hydrophobic foam prepared from a polyether polyol.
2. Background
Polyurethane foams and their methods of manufacture are well known. These foams have a large number of applications including: cushioning for furniture and bedding, including mattresses and topper pads; padding for underlying carpets; seals and gaskets for a variety of uses; acoustical applications; textile laminates; and energy absorbing materials. In particular, hydrophobic polyurethane foams provide a material useful for resisting water penetration in applications such as gaskets and seals. Several approaches have been attempted to produce hydrophobic polyurethane foams.
One method of rendering a polyurethane foam hydrophobic is by impregnating the foam with a hydrophobic agent such as asphalt. Typically, when preparing foams according to this method, the hydrophobic agent in a volatile solvent is added to the prepared foam and the solvent is allowed to evaporate. This method suffers from the drawback of using large amounts of volatile solvents which, when evaporated, may present environmental hazards. In addition, the volatile solvent may affect the physical properties and feel of the foam. In a variation of this technique, an aqueous dispersion of the hydrophobic substance is used to impregnate the foam. However, formation of an aqueous dispersion requires the use of an emulsifier prior to addition to the foam. This method suffers problems because the emulsifier remains in the foam after treatment. The emulsifier in the foam may adversely affect the physical properties or feel of the foam causing problems similar to those experienced when using a volatile solvent.
Alternatively, hydrophobic constituents such as asphalt derivatives may be incorporated into the foam structure during manufacture. For example, the hydrophobic substance may be incorporated by being present during foam formation or during the molding process. Again, however, these methods produce foams with altered physical properties that may not be suitable for particular applications.
Another approach, described in U.S. Pat. No. 4,264,743 to Maruyama et al., assigned to NHK Spring Co., Ltd. of Japan, utilizes a polyester polyol based on dimer acid or castor oil as the major polyol component and other additives such as a blowing agents, a foam stabilizer, a catalyst and, optionally, a lipophilic filler. Such foams are marketed under the name Super Seal(copyright) by, for example, Recticel in Europe and Foamex in the United States. These polyester polyol based polyurethane foams exhibit good hydrophobicity, but suffer from hydrolytic instability due to the nature of the polyester material. In addition, these foams frequently have relatively high densities, for example, over 3 pounds for cubic foot. Thus, the cost of these foams per unit volume tends to be high.
Propylene oxide and propylene oxide/ethylene oxide polyether polyol (hereinafter xe2x80x9cPO/EO polyether polyolxe2x80x9d) blends are used to manufacture polyether polyols for making polyether polyurethane foams. These foams are typically characterized by good cushioning properties and excellent hydrolytic stability. Furthermore, the polyether polyols based on a PO/EO blend will have better processing characteristics that translate into higher yields and better quality foams. It would thus be desirable, in terms of hydrolytic stability and high quality foams, to produce hydrophobic polyurethane foams for, among other applications, use in seals and gaskets based on PO/EO polyether polyols. Attempts to produce highly hydrophobic foams from this system in the past have been unsuccessful.
The present invention overcomes the drawbacks in the art described above. The foam of the present invention has both good hydrophobic properties and good hydrolytic resistance; its relatively low density translates into a low cost polyurethane foam.
The invention relates to a hydrophobic polyurethane foam prepared from a PO/EO polyether polyol, a graft polyol and a hydrophobicity inducing surfactant. The present invention is also a hydrophobic polyurethane foam prepared from a PO/EO polyether polyol and a graft polyol, the foam being sufficiently hydrophobic to pass stringent water impermeability tests, for example, tests used by GM and Ford in the automotive industry and described in detail below (hereafter sometimes collectively referred to as the xe2x80x9cautomotive type testsxe2x80x9d). Preferred foams are sufficiently hydrophobic to pass a water impermeability test for at least 60 minutes, more preferred foams for at least 90 minutes, and the most preferred foams are sufficiently hydrophobic to pass a stringent water impermeability test for at least 24 hours. Graft polyols useful in preparing the inventive foams typically comprise polystyrene and/or polyacrylonitrile grafted onto or dispersed into a PO/EO polyether backbone structure. In a preferred foam, the graft polymer comprises about 60% of a PO/EO polyether backbone, about 30% polystyrene and about 10% polyacrylonitrile. A preferred foam is formed from about 80 parts graft polyol and about 20 parts PO/EO polyether polyol.
The foams of the invention are also prepared using a surfactant, particularly a hydrophobicity inducing surfactant. Typically, hydrophobicity inducing surfactants are polysiloxane-polyalkylene oxide copolymers, usually the non-hydrolyzable polysiloxane-polyalkylene oxide copolymer type. Hydrophobicity inducing surfactants include: Goldschmidt Chemical Corp. of Hopewell, Va. products sold as B8110, B8229, B8232, B8240, B8870, B8418, B8462; Organo Silicons of Greenwich, Conn. products sold as L6164, L600 and L626; and Air Products and Chemicals, Inc. products sold as DC5604 and DC5598. Preferred surfactants are B8870, B8110, B8240, B8418, B8462, L626, L6164, DC5604 and DC5598. B8870 and B8418 from Goldschmidt Chemical Corp. are more preferred; B8418 is most preferred. Polyisocyanates are preferably added at a polyisocyanate index of from about 75 to about 125. Toluene diisocyanate is a preferred polyisocyanate, preferably at a TDI index of about 100. Typically, the inventive foams have an air flow of from about 0.01 to about 3.0 ft3/ft2/min and a density of no more that about 4.0 lb/ft3. The inventive foams may also contain typical polyurethane foam additives such as, for example, catalyst, dye, blowing agent and fire retardant.
In another aspect, the hydrophobic polyurethane foams of the invention are made up of polyol segments derived from a graft polyol and polyol segments derived from a PO/EO polyether polyol and prepared using a hydrophobicity inducing surfactant.
In another aspect, the invention is a hydrophobic polyurethane foam produced by the process of combining a polyisocyanate with a PO/EO polyether polyol and a graft polyol, and allowing the polyisocyanate and polyols to react in the presence of a surfactant to form a foam that is sufficiently hydrophobic to pass a stringent water impermeability test, preferably for at least 60 minutes, more preferably for at least 90 minutes and most preferably for at least 24 hours, with substantially no leaks of water through or into the foam.
In yet another aspect, the foams of the present invention may be formed into a manufactured article, for example, cushioning, padding, a seal such as an automotive seal and a gasket such as an automotive gasket.
Further objectives and advantages would become apparent from consideration of the description and examples that follow.